The present invention relates to the field of variable resistors and potentiometers, and more particularly to multiple-wire brush contacts therefor, and a method for making such contacts.
The preferred form of sliding contact, for engaging the resistance element in potentiometers and in many resistors, is formed of a large number of very fine gage metal wires that are held together and bent to form a multiple-wire brush.
A number of difficulties exist in the manufacture of these wire brush contacts. First, the wires need to be joined in some manner so as to be securely held and at the same time be given the proper electrical conductivity properties relative to one another. Also, because these wires are of such fine gage, they are difficult to handle. Moreover, while welding is the most evident way of securing the wires, great care must be taken so that the heat of welding does not alter the mechanical properties of the wires. Once the wires are held and bent to form a contact spring, a suitable way must be found to securely mount the contact in the potentiometer or resistor.
A wide variety of methods for making wire-brush contacts have been proposed. As an example, U.S. Pat. No. 4,186,483 to Laube et al. discloses forming a multiple-wire brush contact that is staked into a rotor blank. According to Laube a continuous strip of metal is stamped to form "L" shaped cross bars with a pair of weld projections. Multiple-metal wires are placed side-by-side over the cross bars and welded to the weld projections. The wires are cut from adjacent cross bars and bent to form a brush contact, and thereafter the L-portion of the cross bar is severed and discarded as scrap. Finally, a rotor blank is positioned under the contact, which is cut from the continuous strip and pushed directly into a slot in the rotor.
While the Laube patent permits continuous manufacture of contact wipers in rotor blanks, it would be desirable to be able to form multiple-wire brush contacts without the need to have the wire brush contact mounted in a blank, but that could still be securely mounted and handled without undue damage to the contact. It would also be desirable to find other methods of manufacturing multiple wire brush contacts that do not require welding to projections, as part of the process.